Class I phosphoinositide 3-kinases (PI3Ks) are now known to regulate cell growth, cell metabolism, cell survival, cell cycle entry and cell movement. Insulin utilizes Class Ia PI3Ks for regulation of glucose homeostasis and impairment in this regulation can result in Type II diabetes. Activating mutations in Class Ia PI3Ks or inactivating mutations in PTEN, a phosphatase that degrades PI3K products, are some of the most frequent events in human cancers and the majority of solid tumors have mutations in some component of the PI3K signaling pathway. PI3K inhibitors are now in clinical trials for treating cancers and for immune suppression and there is optimism about potential benefits, but concern about potential adverse affects. Over the past granting period we have attempted to understand the complex network of PI3K activation and downstream signaling using a combination of biochemical approaches, cell-based studies and mouse genome manipulations. While work from our laboratory and many other laboratories has resulted in considerable progress in understanding this complex signaling network over the past five years, it is clear that there is much to be done. Our goals for the next granting period are focused on uncovering the complexity of Class Ia PI3K regulation and downstream signaling. We will investigate the relative roles of PI-3,4-P2 and PI-3,4,5-P3 in cellular regulation. We have recently found that a phosphatases that degrades PI-3,4-P2 is a tumor suppressor in human solid tumors suggesting that this lipid plays an important role in cell transformation. We will also determine the mechanism by which the p85 regulatory subunit controls Class Ia PI3K signaling. In particular, we will investigate the importance of post-translational modifications we have recently identified on p85alpha. Finally, we will investigate stochastic regulation of the PI3K pathway in epithelial cells. PUBLIC HEALTH RELEVANCE: The PI3K pathway is the most frequently mutated pathway in human cancers. This grant has funded the research that led to the discovery and elucidation of this pathway. The goal of the proposed research is to identify key regulatory components of this pathway in order to uncover new targets for pharmaceutical intervention.